1. Field of the Invention
The present invention relates to a tube incorporated with an X-ray contrast medium. This contrast medium-containing tube is useful as an indwelling needle and catheter.
2. Description of the Prior Art
There is known a tube of polymeric material (like fluoroplastics having good compatibility with living organisms) incorporated with a contrast medium such as barium sulfate and bismuth oxide. This tube is used as an indwelling needle to be pierced into and fixed to a blood vessel for transfusion, because in case the needle is broken by mistake during use, it is easy to locate a broken piece of it in the blood system by radiography owing to the contrast medium contained therein. This tube is also used as a catheter to be inserted into the human body for blood collection from the heart or injection of a medicine into the internal organs, because the contrast medium helps one to bring the catheter to a desired position by radioscopy.
The contrast medium-containing tube of this kind has been known in several types. For example, Japanese Patent Publication No. 49394/1972 discloses the one in which the contrast medium is uniformly dispersed in the tube wall; Japanese Patent Laid-open No. 119263/1981 discloses the one in which the tube wall consists of three resin layers, with the intermediate layer containing a contrast medium; and Japanese Utility Model Laid-open No. 108389/1976 discloses the one in which the contrast medium forms a continuous stripe in the longitudinal direction.
The contrast medium to be incorporated into the tube for the above-mentioned purposes is usually a bismuth compound or barium sulfate. The former produces a better effect than the latter with a smaller amount because of its higher radiopaqueness. Among bismuth compounds, bismuth oxide is the highest in bismuth content and hence the most effective in radiopaqueness. Nevertheless, it is disliked by doctors and patients more than barium sulfate because it takes on a yellow color. Moreover, tubes containing bismuth oxide cannot be distinguished from one another by coloring because of their inherent yellow color.
There are white bismuth compounds such as basic bismuth carbonate and bismuth oxychloride. However, the former has such a low decomposition point that it decomposes, evolving a gas, while the resin composition containing it is processed at a high temperature. The latter is so unstable to heat and light that it becomes discolored in brown by heat during processing and by light after processing. Consequently, they cannot be a substitute for bismuth oxide.
The present inventor carried out extensive studies on making a white contrast medium-containing tube from a resin which needs a high temperature for processing. As the result, a white heat-resistant bismuth compound was found which yields the desired product. (See U.S. application Ser. No. 510,073 filed Apr. 17, 1990, now U.S. Pat. No. 5,085,863 corresponding to Japanese patent application no. 103065/1989.) However, the continued studies revealed that the contrast medium-containing tube based on this white bismuth compound tends to yellow on exposure to light for a long period of time, even though it looks white and contains no bubbles (due to the decomposition of the white bismuth compound) in the production of the tube. In order to eliminate this disadvantage, the present inventor continued his studies, which led to the present invention.